London Irish scrum-half Tomas O'Leary is set to miss the rest of the season with a back injury.

The 29-year-old O'Leary has undergone surgery to his lower back for what the Aviva Premiership club describe as a "degenerative pre-existing injury" that has deteriorated this term.

A statement from the club read: "Tomas has been unavailable for selection since his last appearance for London Irish against Harlequins at Madejski Stadium on October 28. He now faces a four to six months lay-off."

O'Leary, who has won 24 caps for Ireland, joined London Irish on a three-year contract at the start of this season. He previously played for Munster and was selected to tour South Africa with the 2009 British and Irish Lions. But he suffered a broken ankle while playing for Munster against the Scarlets just a month before the three-Test trip, and was then ruled out of the tour.